The invention relates to an improved installation for the anaerobic purification of waste or effluent water comprising particles of decomposable impurities.
The installation comprises a reaction or decomposition zone into which waste water comprising a sludge of impurities is fed.
It is known, that waste water comprising decomposable organic substances can be purified by an anaerobic microbial decomposition process, whereby methane and carbon dioxide are being originated.
The use of this process for the straight purification of waste water, particularly of concentrated industrial effluent water has been tried, but it showed several disadvantages. A stable fermentation process can hardly be obtained, and a useful practice comparable with aerobic purification could not be realised in a technical scale. In the journal "H.sub.2 O" (1974), Nr. 7, pp. 281-289 the state of the art has been given, with a comprehensive literature reference.
It has been described in said publication, page 281, that in using a methane-developing fermentation for the treatment of less concentrated waste water (having 0.1 through 0.5% by weight of organic matter, one of the most important problems is to find a practically acceptable way for rinsing out the sludge. A stable methane-developing fermentation can be accomplished in a continuous way only if the total amount of active bacterial material in the reactor can be maintained at a constantly high level.
On page 283, FIG. 1 of said publication an experimental device is shown, wherein an after-settler-zone next to and at the top of a recipient for the interception of the gas is provided, said recipient at its lower side having a circular opening, which serves as the inlet as well as the outlet of the after-settler. With such a device a stable and continuous process cannot be achieved.
The problems reflected, which relate to the experiences as described with an experimental device having a contents of 16 liters are being still more severe with industrial reactors having a volume of dozens or several hundreds of cubic meters.
In the existing conventional sludge fermentation tanks e.g. a retention period of the entire mixture of about 30 days is a normal feature. For an efficient purification this sludge retention period (i.e. life-time of the sludge) might not be made shorter (at least 10 days, see the above publication, page 287 at the bottom), while at the same time the retention period of the liquid is reduced to several hours (viz. 3 through 6 hours). An effective purification can be achieved in such a short period only if relatively high concentrations of sludge are present in the reactor (i.e. dozens of grams per liter). In order to obtain this, an efficiently working system is necessary, wherein the following requirements are met:
1. The ascending gas bubbles are being collected, and the gas will be removed efficiently, such that no foam or liquid droplets will be entrained.
2. The liquid is separated from the mixture of sludge and liquid in such a way that a substantially sludge-free effluent will be produced.
3. The sludge separated from said liquid will be concentrated and be recycled into the reactor zone at the highest possible rate.
The separation of sludge and effluent in the conventional aerobic purification systems is in general carried out by means of an after-settler separate from the aeration zone, and the thickened-in sludge is recirculated into the aeration zone through a conduct by means of a pump if any or by other means.
Since in aerobic systems considerable sludge formation is obtained, part of the thickened-in sludge is cocurrently removed from the system (gutter sludge).
This is entirely different from anaerobic purification, for the following reasons:
a. In view of minor sludge formation only small amount of sludge has to be removed.
b. There is no need for using a sump of the after-settler in order to obtain a concentrated gutter sludge, since at the bottom of the reactor there exists a very high sludge concentration as a result of the good settling properties of the anaerobic sludge.
c. The retention period of the sludge outside the reactor ought to be restricted to a minimum, because otherwise gas formation and flotation might occur, such that the function of the settler device would become inefficient.
Several attempts to use anaerobic purification on industrial scale have failed, substantially for reasons of the issue mentioned in the last-above page.
It is an object of the present invention to comply with the requirements as mentioned in the above under 1 through 3, without occurrence of flotation and of other problems.
It is a further object of the present invention to obtain the following advantages:
Simple construction
Easiness of access to all constructional parts
Absence of moving constructional parts, including recycling pump devices
Possibility of an optimal adaptation of the installation to the typical properties of a certain envisaged type of waste water and of sludge, as well as to the input charge, by a proper selection of the mutual ratios of dimensions and by a control or adjustment of the inlet-opening or openings of the settler-device.
A continuous process.
Still another object of the present invention is to provide a compact efficient installation for the anaerobic purification of industrial and/or domestic waste waters or effluents.
Other objects will be elucidated by the specification in detail of the invention, by the Figures enclosed and by the claims.